In order to prevent oxygen oxidation of various types of articles that are easily deteriorated or degraded by oxygen, such as foods, beverages, medicinal products, and cosmetics, and to store them for a long time, oxygen absorbers are used for removing oxygen inside the packaging bodies accommodating these articles.
As the oxygen absorber, an oxygen absorber including an iron powder as the base reactive compound is generally used because of its oxygen-absorbing ability, easiness in handling, and safety. The iron-based oxygen absorber is, however, responsive to a metal detector, and it is therefore difficult to use a metal detector for inspection of foreign matters. Furthermore, packaging bodies containing iron-based oxygen absorbers cannot be heated by a microwave oven because of a risk of ignition. Moreover, since the oxidation reaction of an iron powder needs water, the oxygen-absorbing effect is exhibited only when moisture-rich articles are stored.
Packaging containers and other containers having improved gas barrier properties and an oxygen-absorbing function have been developed by making the containers by a multilayer material including an oxygen-absorbing layer of an oxygen-absorbing resin composition composed of a thermoplastic resin and an iron-based oxygen absorber blended therein (see Patent Literature 1). Specifically, the oxygen-absorbing multilayer film includes an oxygen-absorbing layer disposed between the layers of a conventional gas barrier multilayer film composed of a heat sealing layer and a gas barrier layer, with an intermediate layer of a thermoplastic resin between the oxygen-absorbing layer and each of the layers of the conventional gas barrier multilayer film, depending on the case. The oxygen-absorbing layer is a thermoplastic resin layer dispersing an oxygen absorber therein. The oxygen-absorbing multilayer film is used as a film having the function of absorbing oxygen inside a container in addition to the function of preventing oxygen permeation from the outside and is produced by a known production method, such as extrusion lamination, coextrusion lamination, or dry lamination. However, this oxygen-absorbing multilayer film also similarly has disadvantages: The multilayer film is detected by a metal detector for foreign matter inspection of foods, etc., cannot be heated by a microwave oven, and shows the effect only on moisture-rich articles to be stored. The oxygen-absorbing multilayer film also has a disadvantage of insufficient internal visibility due to its opacity. An oxygen-absorbing multilayer film containing an oxygen absorber such as an iron powder has disadvantages: The multilayer film is detected by a metal detector for foreign matter inspection of foods, etc., has insufficient internal visibility due to its opacity, and reduces flavor when the contents are alcoholic beverage due to generation of aldehyde by oxidation reaction of alcohol using iron as a catalyst.
In the aforementioned circumstances, an oxygen absorber including an organic material as a base reactive compound has been demanded. An oxygen absorber including ascorbic acid as the base compound is known as an oxygen absorber including an organic material as a base reactive compound (see Patent Literature 2).
Meanwhile, an oxygen-absorbing resin composition composed of a resin and a transition metal catalyst is known. For example, a resin composition composed of a polyamide as an oxidizable organic component, in particular, a xylylene group-containing polyamide, and a transition metal catalyst is known (see, Patent Literatures 3 and 4). Patent Literatures 3 and 4 exemplify oxygen absorbers, packaging materials, and multilayer laminate films for wrapping prepared by molding such resin compositions.
An oxygen-absorbing resin composition composed of a resin having a carbon-carbon unsaturated bond and a transition metal catalyst is also known as an oxygen-absorbing resin composition not requiring moisture for absorbing oxygen (see Patent Literature 5).
Furthermore, a composition composed of a polymer containing a substituted cyclohexene functional group or a low molecular-weight substance bonded to the cyclohexene functional group and a transition metal is known as a composition for trapping oxygen (see Patent Literature 6).
Meanwhile, injection molding can produce a molded product having a complicated shape and also has high productivity and is therefore widely diffused in production, for example, machine parts, automobile parts, electric/electronic parts, and containers for foods and medicines. Recently, a variety of types of plastic containers have been widely used as packaging containers because of their advantages such as lightness, transparency, and easiness in molding. As typical plastic containers, for example, injection-molded products having a screw shape at the mouth stopper so that the lid can be sufficiently fastened have been widely employed in containers for beverages.
Examples of the material used in the injection-molded product may include generic thermoplastic resins such as polyolefins (e.g., polyethylene and polypropylene), polyesters, and polystyrenes. In particular, injection-molded products mainly composed of polyesters such as poly(ethylene terephthalate) (PET) are widely used as plastic containers for beverages such as tea, fruit juice beverages, carbonated beverages, and alcoholic beverages. Although injection-molded products mainly composed of thermoplastic resins are excellent as packaging materials, they apt to allow oxygen to permeate from the outside, unlike glass bottles and metal containers, and therefore have a problem in the performance of storing contents packaged in a hermetically closed condition. Accordingly, in order to provide a gas barrier property to such an injection-molded product of a generic resin, injection-molded products each having a gas barrier layer as an intermediate layer have been practically used.
Incidentally, for example, glass ampoules, vials, and prefilled syringes have been conventionally used as medical packaging containers for packaging and storing drug solutions in a hermetically closed condition. These glass containers, however, have problems: sodium ions and other components elute into the solution of the contents inside the container during storage; micro substances called flakes occur; when a light-shielding glass container colored with a metal is used, the contents are contaminated by the metal for coloring; and the container is easily broken by a shock such as falling. In addition to these problems, since glass containers have a relatively large specific gravity, medical packaging containers are disadvantageously heavy. Therefore, development of alternate materials has been demanded. Specifically, plastics lighter than glass, for example, polyester, polycarbonate, polypropylene, and cycloolefin polymers, have been investigated as glass alternatives.
For example, a medical container made of a polyester-based resin material has been proposed (see Patent Literature 7).
Meanwhile, a plastic multilayer container including a gas barrier layer as an intermediate layer for providing a gas barrier property to the container has been investigated. Specifically, a prefilled syringe including the innermost layer and the outermost layer of a polyolefin-based resin and an intermediate layer of a resin composition having an excellent oxygen barrier property and thereby having an enhanced oxygen barrier property has been proposed (see Patent Literature 8). Furthermore, a multilayer container prepared by laminating a gas barrier layer on a resin layer has been investigated, where the gas barrier layer is made of, for example, a polyamide prepared from metaxylylenediamine and adipic acid (hereinafter, may be referred to as “nylon MXD6”), an ethylene-vinyl alcohol copolymer, polyacrylonitrile, poly(vinylidene chloride), aluminum foil, a carbon coat, or a vapor-deposited inorganic oxide.
Furthermore, in recent years, nylon MXD6 provided with an oxygen-absorbing function by being mixed with a small amount of a transition metal compound has been proposed to be used as an oxygen barrier material constituting containers or packaging materials (see Patent Literature 9).
Furthermore, examples of the medical container may include artificial kidney hemodialyzers (dialyzers), in addition to ampoules, vials, and syringes. For the housing of a dialyzer, transparent plastic allowing the contents to be well seen from the outside, such as polystyrene or polycarbonate, is used, and polycarbonate having excellent shock resistance is more preferably used in order to avoid breakage due to falling or other shocks (see Patent Literature 10).